This renewal proposal is a proposed continuation of the collaborative efforts between the laboratory of Prof. David C. Baker and that the Prof. Robert J. Suhadolnik to elucidate the biosynthetic pathways to a group of medicinally important nucleosides, which includes ara-A and 2'- deoxycoformycin (2'-dCF). The former is a clinically useful antiviral (antiherpes agent), and the latter is a potent inhibitor of adenosine deaminase that has recently been found to be of clinical utility in the treatment of hairy-cell leukemia. Goals of the current proposal are to (1) Conclude our studies on the biosynthesis of ara-A by defining the mechanism for the 2'-epimerization of adenosine, which is currently postulated to be either a free-radical process or one which involves NAD in a redox process. Detailed studies on the enzyme, adenosine 2'- epimerase, including the probing of its active site with photoaffinity labels and the cloning of the gene for the enzyme, are planned. (2) Elucidate the precise pathway by which adenosine is converted to 2'-dCF. Plans are outlined whereby intermediates in the biosynthesis will be isolated and fully characterized via modern spectroscopic methods, with the assistance of compounds labeled with stable isotopes. Such studies will serve to elucidate the pathways to other nucleosides in the 2'-dCF family, including 2'-chloro-2'-deoxycoformycin and coformycin. Interrelationships in the biosynthetic pathways among these analogues will be discerned. The mechanism for chlorination of CF to give 2'-CldCF will be determined. The enzyme, 8-keto-2'-dCF reductase, which reduces 8- ketodeoxycoformycin to 2'-dCF will be studied in detail, with the aim of probing the active site with photoaffinity labels and cloning the gene for producing the enzyme into S. lividans. The latter is considered of possible utility in producing 2'-dCF via the currently available chemical synthesis which involves a nonspecific reduction of the 8-keto-2'-dCF. (3) Elucidate the biosynthesis of a group of related compounds which includes adecypenol, a cyclopentenyl analogue of 2'-dCF; azepinomycin, a 1,4-diazepine; and nucleocidin, a fluorosugar-containing nucleoside.